Sustaining power levels of optical signals in optical networks presents substantial technical challenges. It is desirable for the power of the signals to be within a dynamic range of the receivers in an optical network, and the dynamic range of the receivers tends to be smaller for higher data rates. Consequently, it is important to employ an accurate method for assessing the necessary level of amplification in nodes in an optical network.
One method for determining the amplifier gain for a signal is to measure a pilot tone. One example of a pilot tone system is the Mitsubishi Electric System described by Motoshima et al. in the Journal of Lightwave Technology, vol. 19, page 1759 (2001). The pilot tone is a dummy channel located within the same band as information-carrying channels in an optical signal. The power of the pilot tone is measured to indicate the overall power level of the signal. But the pilot tone only provides a power measurement from one channel, and the pilot tone channel may not be used to carry information.
An alternative method is the use of telemetry to communicate power levels. In the telemetry method, information about the number of provisioned channels is communicated to each node, along with information about the number of nodes through which the signal has passed. The number of channels is used to compute an expected output power level, while the number of nodes is used to analyze the amount of accumulated amplified spontaneous emission (ASE), a form of noise resulting from stimulated amplification of the spontaneous emission in an amplifier gain medium. Telemetry relies upon calculations, such as ASE calculations, that may not be completely accurate, and can vary in actual network conditions. Furthermore, the uncertainties may accumulate so that the error is more significant in networks with a large number of nodes.